Process for Aromatic Alkylation

ABSTRACT

This invention relates to a process for the selective alkylation of toluene and/or benzene with an oxygen-containing alkylation agent. In particular, the process uses a selectivated molecular sieve which has been modified by the addition of a hydrogenation component, wherein at least one of the following conditions is met: (a) the selectivated molecular sieve has an alpha value of less than 100 prior to the addition of the hydrogenation component, or (b) the selectivated and hydrogenated catalyst has an alpha value of less than 100. The process of this invention provides high selectivity for the alkylated product while reducing catalyst degradation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional Application No.60/533,951, filed Dec. 31, 2003, the disclosure of which is incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates to a process for the selective alkylationof toluene, benzene, naphthalene, alkyl naphthalene and mixtures thereofwith an oxygen-containing alkylation agent. In particular, the processuses a catalyst comprising a selectivated molecular sieve which has beenmodified by the addition of at least one hydrogenation component,wherein at least one of the following conditions is met: (a) theselectivated molecular sieve has an alpha value of less than 100 priorto the incorporation the hydrogenation component, or (b) theselectivated and hydrogenated molecular sieve used in the selectivealkylation process has an alpha value of less than 100. The process ofthis invention provides high selectivity for the alkylated product whilereducing catalyst deactivation.

BACKGROUND OF THE INVENTION

Of the xylene isomers, i.e. ortho-, meta-, and para-xylenes, thepara-xylene isomer is of particular value as a large volume chemicalintermediate. One method for manufacturing para-xylene is bydisproportionation of toluene into xylenes. However, a disadvantage ofthis process is that large quantities of benzene are also produced.Another process for manufacturing para-xylene is the isomerization of afeedstream that contains non-equilibrium quantities of mixed ortho- andmeta-xylene isomers and is lean with respect to para-xylene content. Adisadvantage of this process is that the separation of the para-xylenefrom the other isomers is expensive.

There is growing interest in the alkylation of toluene with methanol asa next generation method for producing para-xylene. This technology cantheoretically produce twice the yield of para-xylene from toluene,compared to the toluene disproportionation process. Examples of suchtoluene methylation processes include U.S. Pat. No. 3,965,207, whichinvolves the methylation of toluene with methanol using a molecularsieve catalyst such as ZSM-5. U.S. Pat. No. 4,670,616 involves theproduction of xylenes by the methylation of toluene with methanol usinga borosilicate zeolite catalyst which is bound by a binder such asalumina, silica, or alumina-silica.

A disadvantage of known toluene methylation catalysts is that methanolselectivity to para-xylene, the desirable product, has been low, in therange of 50-60%. The balance is wasted on the production of coke andother undesirable products. Attempts to increase the para-xyleneselectivity have been conducted, however, it has been found that aspara-xylene selectivity increases, the lifespan of the catalystdecreases. It is believed that the rapid catalyst deactivation is due tobuild up of coke and heavy by-products on the catalyst. The limitedcatalyst lifespan typically necessitates the use of a fluidized bedreactor wherein the catalyst is continuously regenerated. However, sucha system usually requires high capital investment. A preferred systemfor toluene methylation is to use a fixed bed reactor because of lowercapital investment. However, until a suitable catalyst is found thatprovides a sufficient lifespan, with a sufficient selectivity to thedesired product, fixed bed systems are simply impractical. There remainsa need for an improved toluene methylation process having a catalyticsystem that minimizes or avoids the disadvantages of prior systems,which includes low para-xylene selectivity and rapid catalystdeactivation. The present invention satisfies this need.

SUMMARY OF THE INVENTION

The invention is a process for forming a selectively alkylated aromaticcompound comprising reacting an alkylating agent with a feed comprisingan aromatic compound selected from the group consisting of toluene,benzene, naphthalene, alkyl naphthalene and mixtures thereof in thepresence of a catalyst under alkylation reaction conditions, saidcatalyst comprising a selectivated molecular sieve and at least onehydrogenation metal, wherein at least one of the following conditions issatisfied: (a) the selectivated molecular sieve has an alpha value ofless than 100 prior to incorporation of said at least one hydrogenationmetal, or (b) the selectivated and hydrogenated molecular sieve has analpha value of less than 100.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1-12 and 14-18 are plots showing the para-selectivity of variouscatalysts in a toluene methylation process.

FIG. 13 is a graph showing the effect of hydrogenation metals, water andphosphorus on reducing methanol decomposition in a toluene methylationprocess.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for the selective alkylationof toluene, benzene, naphthalene, alkyl naphthalene and mixtures thereofwith an oxygen-containing alkylation agent. The process uses a catalystcomprising a selectivated molecular sieve, preferably a para-selectivemolecular sieve, that has been modified by the addition of at least onehydrogenation component. In accordance with this invention, at least oneof the following conditions should also be met: (a) the selectivatedmolecular sieve has an alpha value of less than 100 prior to theincorporation of the hydrogenation component, or (b) the selectivatedand hydrogenated molecular sieve has an alpha value of less than 100.The catalyst, when used in this process, has an extended catalystlifetime, while providing para-selectivity of greater than 60%, morepreferably greater than 75%, more preferably greater than 80%, even morepreferably greater than 85% and most preferably greater than 90%.Preferably, the process is a toluene or benzene methylation process,which forms para-xylene at these preferred para-selectivity ranges.

Catalysts suitable for use in the present invention include any catalystthat is effective for the alkylation of toluene, benzene, naphthalene,alkyl naphthalene or mixtures thereof. Preferably, the catalyst will beeffective for the preferred process of toluene or benzene methylation.Catalysts used in the present invention include naturally occurring andsynthetic crystalline molecular sieves. Examples of such molecularsieves include large pore molecular sieves, intermediate size poremolecular sieves, and small pore molecular sieves. These molecularsieves are described in “Atlas of Zeolite Framework Types”, eds. Ch.Baerlocher, W. H. Meier, and D. H. Olson, Elsevier, Fifth Edition, 2001,which is hereby incorporated by reference. A large pore molecular sievegenerally has a pore size of at least about 7 Å and includes IWW, LTL,VFI, MAZ, MEI, FAU, EMT, OFF, *BEA, and MOR structure type molecularsieves (IUPAC Commission of Zeolite Nomenclature). Examples of largepore molecular sieves, include ITQ-22, mazzite, offretite, zeolite L,VPI-5, zeolite Y, zeolite X, omega, Beta, ZSM-3, ZSM-4, ZSM-18, ZSM-20,SAPO-37, and MCM-22. An intermediate pore size molecular sieve generallyhas a pore size from about 5 Å to about 7 Å and includes, for example,ITH, ITW, MFI, MEL, MTW, EUO, MTT, HEU, FER, MFS, and TON structure typemolecular sieves (IUPAC Commission of Zeolite Nomenclature). Examples ofintermediate pore size molecular sieves, include ITQ-12, ITQ-13, ZSM-5,ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, ZSM-57,silicalite, and silicalite 2. A small pore size molecular sieve has apore size from about 3 Å to about 5 Å and includes, for example, CHA,ERI, KFI, LEV, and LTA structure type molecular sieves (IUPAC Commissionof Zeolite Nomenclature). Examples of small pore molecular sievesinclude ZK-4, SAPO-34, SAPO-35, ZK-14, SAPO-42, ZK-21, ZK-22, ZK-5,ZK-20, zeolite A, erionite, chabazite, zeolite T, gmelinite, andclinoptilolite.

The intermediate pore size molecular sieve will generally be acomposition having the following molar relationship:

X₂O₃:(n)YO₂

wherein X is a trivalent element such as aluminum, iron, boron, and/orgallium and Y is a tetravalent element such as silicon, tin, and/orgermanium; and n has a value greater than 12, said value being dependentupon the particular type of molecular sieve and the desired alpha valueof the molecular sieve, in accordance with this invention. When theintermediate pore size molecular sieve is a MFI structure type molecularsieve, n is preferably greater than 10 and preferably, from 20:1 to200:1.

In accordance with this invention, the molecular sieve catalyst isselectivated for the production of the desired alkylated product, whichin the preferred embodiment is para-xylene. The catalyst can beselectivated by treating its surface with compounds of phosphorus and/ormagnesium and/or various metal oxides such as alkaline earth metaloxides, e.g., calcium oxide, magnesium oxide, etc. rare earth metaloxides, lanthanum oxide, and other metal oxides such as boron oxide,titania, antimony oxide, and manganese oxide. Preferred ranges for suchtreatment are from about 0.1 wt. % to 25 wt. %, more preferably fromabout 1 wt. % to about 10 wt. % of such compounds based on the weight ofthe catalyst. The selectivation may also be accomplished by depositingcoke on the catalyst. Coke selectivation can be carried out during themethylation reaction, such as by running the methylation reaction atconditions which allow the deposition of coke on the catalyst. Also, thecatalyst can be preselectivated with coke, for example, by exposing thecatalyst in the reactor to a thermally decomposable organic compound,e.g., benzene, toluene, etc. at a temperature in excess of thedecomposition temperature of said compound, e.g., from about 400° C. toabout 650° C., more preferably 425° C. to about 550° C., at a WHSV inthe range of from about 0.1 to about 20 lbs. of feed per pound ofcatalyst per hour, at a pressure in the range of from about 1 to about100 atmospheres, and in the presence of 0 to about 2 moles of hydrogen,more preferably from about 0.1 to about 1 moles of hydrogen per mole oforganic compound, and optionally in the presence of 0 to about 10 molesof nitrogen or another inert gas per mole of organic compound. Thisprocess is conducted for a period of time until a sufficient quantity ofcoke has deposited on the catalyst surface, generally at least about 2%by weight and more preferably from about 8% to about 40% by weight ofcoke.

A silicon compound may also be used to selectivate the catalyst. Thesilicon compound may comprise a polysiloxane including silicones, asiloxane, and a silane including disilanes and alkoxysilanes. As isknown to those of ordinary skill in the art, multiple treatments may beemployed to effect various degrees of selectivation.

Silicones that can be used to selectivate the catalyst include thefollowing:

wherein R₁ is hydrogen, fluoride, hydroxy, alkyl, aralkyl, alkaryl orfluoro-alkyl. The hydrocarbon substituents generally contain from 1 toabout 10 carbon atoms and preferably are methyl or ethyl groups. R₂ isselected from the same group as R₁, and n is an integer of at least 2and generally in the range of 2 to about 1000. The molecular weight ofthe silicone employed is generally between about 80 to about 20,000 andpreferably about 150 to about 10,000. Representative silicones includedimethylsilicone, diethylsilicone, phenylmethylsilicone, methylhydrogensilicone, ethylhydrogensilicone, phenylhydrogensilicone,fluoropropylsilicone, ethyltrifluoroprophysilicone, tetrachlorophenylmethyl methylethylsilicone, phenylethylsilicone, diphenylsilicone,methyltrisilicone, tetrachlorophenylethyl silicone, methylvinylsiliconeand ethylvinylsilicone. The silicone need not be linear but may becyclic as for example hexamethylcyclotrisiloxane,octamethylcyclotetrasiloxane, hexaphenyl cyclotrisiloxane andoctaphenylcyclotetrasiloxane. Mixtures of these compounds may also beused as well as silicones with other functional groups.

Useful siloxanes and polysiloxanes include as non-limiting examplehexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, octamethylrisiloxane,decamethyltetrasiloxane, hexaethylcyclotrisiloxane, octaethylcyclotetrasiloxane, hexaphenylcyclotrisiloxane andoctaphenylcyclo-tetrasiloxane.

Useful silanes, disilanes, or alkoxysilanes include organic substitutedsilanes having the general formula:

wherein R is a reactive group such as hydrogen, alkoxy, halogen,carboxy, amino, acetamide, trialkylsilyoxy, R₁, R₂ and R₃ can be thesame as R or can be an organic radical which may include alkyl of from 1to about 40 carbon atoms, alkyl or aryl carboxylic acid wherein theorganic portion of alkyl contains 1 to about 30 carbon atoms and thearyl group contains about 6 to about 24 carbons which may be furthersubstituted, alkylaryl and arylalkyl groups containing about 7 to about30 carbon atoms. Preferably, the alkyl group for an alkyl silane isbetween about 1 and about 4 carbon atoms in chain length. Mixtures mayalso be used.

The silanes or disilanes include, as non-limiting examples,dimethylphenylsilane, phenylrimethylsilane, triethylsilane andhexamethyldislane. Useful alkoxysilanes are those with at least onesilicon-hydrogen bond.

In a preferred embodiment, the molecular sieve catalyst is selectivatedusing the combined selectivation techniques of contacting the molecularsieve with a silicon compound and treatment with magnesium and/orphosphorus.

Usually the molecular sieve will be incorporated with binder materialresistant to the temperature and other conditions employed in theprocess. Examples of suitable binder material include clays, alumina,silica, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The molecularsieve may also be composited with zeolitic material such as the zeoliticmaterials that are disclosed in U.S. Pat. No. 5,993,642.

The relative proportions of molecular sieve and binder material willvary widely with the molecular sieve content ranging from between about1 to about 99 percent by weight, more preferably in the range of about10 to about 70 percent by weight of molecular sieve, and still morepreferably from about 20 to about 50 percent.

Catalysts particularly suited for the methylation reaction are zeolitebound zeolite catalysts. These catalysts, as well as their method ofpreparation, are described in U.S. Pat. No. 5,994,603, which is herebyincorporated by reference. The zeolite bound zeolite catalysts willcomprise first crystals of an acidic intermediate pore size firstmolecular sieve and a binder comprising second crystals of a secondmolecular sieve. Preferably, the zeolite bound zeolite catalyst containsless than 10 percent by weight based on the total weight of the firstand second zeolite of non-zeolitic binder, e.g., amorphous binder. Anexample of such a catalyst comprises first crystals of a MFI or MELstructure type, e.g., ZSM-5 or ZSM-11, and a binder comprising secondcrystals of MFI or MEL structure type, e.g., Silicalite 1 or Silicalite2.

Hydrogenation metals useful in accordance with this invention encompasssuch metal or metals in the elemental state (i.e. zero valent) or insome other catalytically active form such as an oxide, sulfide, halide,carboxylate and the like. Preferably, the metal is used in its elementalstate. Examples of suitable hydrogenation metals include Group VIIIAmetals (i.e., Pt, Pd, Ir, Rh, Os, Ru, Ni, Co and Fe), Group IVB metals(i.e., Sn and Pb), Group VB metals (i.e., Sb and Bi), and Group VIIAmetals (i.e., Mn, Tc and Re). Noble metals (i.e., Pt, Pd, Ir, Rh, Os andRu) are sometimes preferred, most preferably Rh. The hydrogenationcomponent may also be accompanied by another metal promoter.

The amount of Group VIIIA hydrogenation metal present on the catalystwill usually be from about 0.1 wt. % to about 5 wt. % of hydrogenationmetal based on the weight of the catalyst. The incorporation of thehydrogenation metal can be accomplished with various techniques known tothose skilled in the art. For example, the metal can be incorporatedinto the catalyst by impregnation, or by ion exchange of an aqueoussolution containing the appropriate salt, or by a combination of thesemethods. By way of example, in an ion exchange process, platinum can beintroduced by using cationic platinum complexes such astetraammine-platinum (II) nitrate. In addition, the hydrogenationfunction can be present by physical intimate admixing, that is, thehydrogenation function can be physically mixed or extruded with theactive catalyst. Physical intimate admixing can also be conducted byincorporating the hydrogenation function on a particle separate from theactive catalyst, and then the particle carrying the hydrogenationfunction placed in close proximity to the catalyst. For example, thehydrogenation metal can be impregnated onto an amorphous support that isco-mingled with the active molecular sieve catalyst such as described inU.S. Pat. No. Re. 31,919 to Butter et al., incorporated by referenceherein.

Typical alkylating agents include methanol, dimethylether,methylchloride, methylbromide, methylcarbonate, acetaldehyde,dimethoxyethane, acetone, and dimethylsulfide. For a toluene or benzenemethylation process, the preferred methylating agents are methanol anddimethylether. The methylating agent can also be formed from synthesisgas, e.g., the agent can be formed from the H2, CO, and/or CO2 ofsynthesis gas. The methylating agent can be formed from the synthesisgas within the methylation reaction zone. One skilled in the art willknow that other methylating agents may be employed to methylate thebenzene and/or toluene based on the description provided therein.

In accordance with this invention, either (a) the selectivated molecularsieve or (b) the selectivated and hydrogenated molecular sieve used inthe alkyating process will have an alpha value of less than 100, morepreferably less than 50, even more preferably less than 25, and mostpreferably less than 10. As used herein, the alpha value is ameasurement of the Bronsted acid activity of the selectivated molecularsieve, i.e. it discounts the effects of the addition of thehydrogenation component on the alpha value of the molecular sieve. Thealpha test is described in U.S. Pat. No. 3,354,078 and in the Journal ofCatalysis, Vol. 4, 522-529 (1965); Vol. 6, 278 (1966); and Vol. 61, 395(1980), each incorporated herein by referenced. The experimentalconditions of the alpha test preferably include a constant temperatureof 538° C. and a variable flow rate as described in detail in theJournal of Catalysis, Vol. 61, 395 (1980). Typically, molecular sieveshaving a higher silica to alumina ratio will have a lower alpha value.Regardless, the alpha activity of a catalyst can be reduced inaccordance with techniques known to those of ordinary skill in the art.For example, the alpha activity of a catalyst may be reduced by (1)steaming the catalyst at appropriate conditions, or (2) ion exchangingthe catalyst with cations such as alkali metal ions.

The alkylation reaction can be carried out in vapor phase. Reactionconditions suitable for use in the present invention includetemperatures from about 300° C. to about 700° C. and preferably about400° C. to about 700° C. The reaction is preferably carried out at apressure from about 1 to 1000 psig, more preferably from about 1 to 150psig, and even more preferably about 1 to 50 psig. The reaction ispreferably carried out at a weight hourly space velocity of betweenabout 0.1 and about 200, more preferably between about 1 to about 20,and even more preferably between about 6 and 12, and preferably betweenabout 1 and about 100 weight of charge per weight of catalyst per hour.The molar ratio of toluene and benzene to alkylating agent can vary andwill usually be from about 0.1:1 to about 20:1. Preferred ratios foroperation are in the range of 2:1 to about 4:1. The alkylating agent isusually supplied to the reaction zone through multiple feed points,e.g., 3-6 feed points. The process is preferably conducted in thepresence of hydrogen at a partial pressure of at least 5 psi.Preferably, the system also includes water added to the feed, such thatthe molar ratio of hydrogen and/or added water to the aromatic compoundand alkylating agent in the feed is between about 0.01 to about 10.

In an embodiment, the molecular sieve used in accordance with thisinvention has a hydrogenation metal comprising rhodium. The use ofrhodium as the hydrogenation component has been found to reduce theamount of synthesis gas formed due to the decomposition of thealkylating agent (i.e. methanol in the preferred embodiment).

In another embodiment, the molecular sieve used in accordance with thisinvention has a hydrogenation metal comprising platinum, and aselectivating compound comprising phosphorus. When such a molecularsieve is used in the process of this invention, and wherein water isco-fed into the reactor, the amount of synthesis gas formed due to thedecomposition of the alkylating agent (i.e. methanol in the preferredembodiment) is found to be reduced.

EXAMPLES Example 1 4× Silica-Selectivated, 0.1% Pt ImpregnatedH-ZSM-5/SiO₂ (Catalyst A)

Silica-bound H-ZSM-5 (0.4 μm, 26:1 Si:Al₂) extrudate (65/35 ZSM-5/SiO₂,1/16″ cylindrical) was impregnated for 0.1 wt. % platinum (Pt) withtetraammine platinum nitrate and calcined at 660° F. This material wasthen selectivated with silica by impregnating with 7.8 wt. % Dow™-550silicone (dimethylphenylmethylpolysiloxane) in decane, stripping thedecane, and calcining at 1000° F. This silica selectivation procedurewas repeated three more times. The final material had an alpha value of255.

Example 2 Steamed, 4× Silica-Selectivated, 0.1% Pt ImpregnatedH-ZSM-5/SiO₂ (Catalyst B)

Silica-bound H-ZSM-5 (0.4 μm, 26:1 Si:Al₂) extrudate (65/35 ZSM-5/SiO₂,1/16″ cylindrical) was loaded with 0.1 wt. % Pt by incipient wetnessimpregnation with tetraammine platinum nitrate, followed by drying at250° F. and calcining for 1 hour in air at 660° F. Theplatinum-containing extrudate was then selectivated with silica byimpregnating with 7.8 wt. % Dow™-550 silicone in decane, stripping thedecane, and calcining. This procedure was repeated three more times. The4× selectivated material was then steamed in 100% steam at atmosphericpressure for 24 hours at 1000° F. The final material had an alpha valueof 17.

Example 3 Steamed, 3× Silica-Selectivated H-ZSM-5/SiO₂ (Catalyst C)

Silica-bound H-ZSM-5 (0.4 μm, 26:1 Si:Al₂) extrudate (65/35 ZSM-5/SiO₂,1/16″ cylindrical) was selectivated with silica by impregnating with 7.8wt. % Dow™-550 silicone in decane, stripping the decane, and calciningat 1000° F. This procedure was repeated two more times. The 3×selectivated material was then steamed in 100% steam at atmosphericpressure for 24 hours at 10001F. The final material had an alpha valueof 15.

Example 4 Steamed, 0.1% Pt Impregnated, 3× Silica-SelectivatedH-ZSM-5/SiO₂ (Catalyst D)

The catalyst of Example 3 was loaded with 0.1 wt. % Pt by incipientwetness impregnation with tetraammine platinum nitrate, followed bydrying at 250° F. and calcining for 3 hours in air at 660° F. Thecatalyst, prior to incorporation of the hydrogenation metal, has alphavalue of 15.

Example 5 Steamed, 3× Silica-Selectivated, 0.1% Pt ImpregnatedH-ZSM-5/SiO₂ (Catalyst E)

Silica-bound H-ZSM-5 (0.4 μm, 26:1 Si:Al₂) extrudate (65/35 ZSM-5/SiO₂,1/16″ cylindrical) was loaded with 0.1 wt. % Pt by incipient wetnessimpregnation with tetraammine platinum nitrate, followed by drying at250° F. and calcining for 3 hours in air at 660° F. Theplatinum-containing extrudate was then selectivated with silica byimpregnating with 7.8 wt. % Dow™-550 silicone in decane, stripping thedecane, and calcining at 1000° F. This procedure was repeated two moretimes. The 3× selectivated material was then steamed in 100% steam atatmospheric pressure for 18 hours at 10001F. The final material had analpha value of 14.

Example 6 Catalytic Evaluations of Catalysts A and B

The following catalytic data were obtained using a downflow fixed-bedreactor with the following operating conditions, unless otherwise noted:Temperature=500° C., Pressure=15 psig, H₂/hydrocarbon molar ratio=0.8,pure methanol and toluene feeds at 1:3 molar ratio, WHSV=3.9 h⁻¹ basedon sieve-containing base case catalyst. The catalyst load was 2 g forthe base catalyst runs. For the 1:3 molar feed mixture, the maximumtoluene conversion expected from reaction with methanol would be about33%. Methanol utilization is reported as (moles of xylene formed−molesof benzene formed)/(moles of methanol converted). Benzene is subtractedto account for any xylene formed by the disproportionation of toluene toxylene plus benzene.

Referring now to FIG. 1, Catalyst A is impregnated with a platinumhydrogenation component, however, the test data indicates poor stabilityat 10 hours. Referring to FIG. 2, the data indicates that impregnationof a hydrogenation component can enhance the catalyst stability for atoluene methylation process, while maintaining high para-xyleneselectivity, when the catalyst has a low alpha value.

Example 7 Catalytic Evaluations of Catalysts C, D, and E

FIGS. 3-5 compare the performance of Catalysts C, D, and E. The datashow that platinum incorporation into the acidic molecular sievecatalysts enhances the catalyst stability, para-xylene selectivity, andmethanol utilization of the toluene methylation reaction, when the alphavalue is within the criteria of this invention.

Example 8 Catalyst F

A 450:1 Si:Al₂ HSLS ZSM-5 molecular sieve is spray dried in asilica/alumina/clay/phosphorus matrix followed by calcination in air at540° C. The base material is then steamed-selectivated at hightemperatures (approximately 1060° C.). The resulting material had analpha value of 2.

Example 9 0.1% Pt impregnated Catalyst F (Catalyst G)

The catalyst of Example 8 was loaded with 0.1 wt. % Pt by incipientwetness impregnation with tetraammine platinum nitrate, followed bydrying at 250° F. and calcining for 3 hours in air at 660° F.

Example 10

The following catalytic data presented were obtained over Catalysts Fand G using a downflow fixed-bed reactor with the following operatingconditions, unless otherwise noted on the figure: Temperature=500-585°C., Pressure=40 psig, H₂/hydrocarbon molar ratio=2, H₂O/hydrocarbonmolar ratio=2, pure methanol and toluene feeds at 1:2 molar ratio,WHSV=2-8 h⁻¹ based on sieve-containing base case catalyst. The catalystload was 2 g. For the 1:2 molar feed mixture, the maximum tolueneconversion expected from reaction with methanol would be about 50%.Methanol utilization is reported as (moles of xylene formed−moles ofbenzene formed)/(moles of methanol converted). Benzene is subtracted toaccount for any xylene formed by the disproportionation of toluene toxylene plus benzene.

The catalytic performance for Catalyst F is shown in FIG. 6. The datashow that the toluene conversion was decreased from 25% to 12% within 13hours on stream.

The catalytic performance of Catalyst G is shown in FIG. 7. The datashow that impregnation of Catalyst F with platinum dramatically enhancesthe catalyst life. The catalyst activity is maintained at 150 hours.

Example 11 Catalyst H

Catalyst H is a zeolite-bound-zeolite having a core zeolite crystalcomprised of ZSM-5 (70-75:1 Si:Al₂) bound with silica (binder content30% of final catalyst), where the silica binder is converted tosilicalite (>900:1 Si:Al₂). The preparation of such azeolite-bound-zeolite is described in U.S. Pat. Nos. 5,665,325 and5,993,642. The final material had an alpha value of 630.

Catalytic data for Examples 11-16 were obtained using a downflowfixed-bed reactor with the following operating conditions, unlessotherwise noted: Temperature=500° C., Pressure=15-150 psig,H₂/hydrocarbon molar ratio=2, pure methanol and toluene feeds at 1:3molar ratio, WHSV=8 hr⁻¹ based on sieve-containing base case catalyst.The catalyst load was 2 g for the base catalyst runs. For the 1:3 molarfeed mixture, the maximum toluene conversion expected from reaction withmethanol would be about 33%. Methanol utilization is reported as (molesof methanol converted)/(moles of xylene formed−moles of benzene formed).Benzene is subtracted to account for any xylene formed by thedisproportionation of toluene to xylene plus benzene.

Referring to FIG. 8, the catalytic performance of the reference CatalystH shows good stability and methanol utilization, but no enhancedpara-selectivity. High initial benzene formation (7%), due to toluenedisproportionation reaction, was obtained. The toluene conversiondeclines with the time on stream. This decline is mainly due to the lossof catalyst activity on the toluene disproportionation reaction. Thebenzene formation decreased from 7% to less than 2% within 24 hours.

Example 12 7 wt. % Mg Impregnated Catalyst H (Catalyst I)

Catalyst H was selectivated with 7 wt. % of magnesium (Mg) in thefollowing manner. Ammonium nitrate hexahydrate (55.4 g) was dissolved in27.95 g deionized water. This solution was slowly added to 100 g ofCatalyst H in a rotary impregnator. The catalyst was dried at ambientconditions overnight. The catalyst was calcined at 660° F. for 3 hoursin full air (3 vol/vol/min). The resulting material had an alpha valueof 20.

Referring now to FIG. 9, magnesium impregnation treatment boosts thepara-xylene selectivity from about 30% to about 60%. However, a slightimpact on the catalyst stability, toluene conversion and methanolutilization is shown. FIG. 9 also shows that higher reaction pressures(150 psig versus 50 psig) result in lower para-xylene selectivity (58%versus 65%).

Example 13 1.5 wt. % P, 7 wt. % Mg Impregnated Catalyst H (Catalyst J)

The catalyst of Example 12 was modified with 1.5 wt. % phosphorus (P),and the resulting material had an alpha value of 37. Referring to FIG.10, Catalyst J was evaluated in a toluene methylation reaction atdifferent hourly space velocities, with and without co-feeding water,and at different reaction temperatures. The data show that increasingthe hourly space velocity from 4 to 8 resulted in higher para-xyleneselectivity (78% versus 63%). In addition, the toluene conversion andmethanol utilization were slightly improved.

Example 14 2.5 wt % P, 7 wt % Mg Impregnated Catalyst H (Catalyst K)

The catalyst of Example 12 was modified with 2.5 wt. % phosphorus, whichresulted in a final material with an alpha value of 37. Referring now toFIG. 11, increasing the phosphorus content over the 1.5 wt. % providedin Example 13 improves the para-xylene selectivity from 75% to 93% atthe same conditions. However the stability of the catalyst is affected,with the higher phosphorus content of this Example 14 deactivating thecatalyst faster than the lower phosphorus content catalyst of Example13.

Example 15 0.1 wt % Rh, 2.5 wt % P, 7 wt % Mg Impregnated Catalyst H(Catalyst L)

The catalyst of Example 14 was modified with 0.1 wt % of rhodium (Rh) asthe hydrogenation component. Rhodium chloride hydrate was dissolved indeionized water. This solution was slowly added to the catalyst ofExample 14 in a rotary impregnator. The catalyst was mixed well and thendried at 250° F. overnight. The catalyst was then calcined in full airat 660° F. for 3 hours (3 vol/vol/min).

As shown in FIG. 12, significant catalyst stabilization was achieved bythe addition of the hydrogenation component, rhodium, while maintaininghigh para-xylene selectivity.

Moreover, as shown in FIG. 13, gas phase analysis indicates that the useof rhodium as the hydrogenation component for a molecular sieve inaccordance with this invention reduces the unwanted methanoldecomposition to synthesis gas, in particular when water is co-fed intothe reactor. As used in FIG. 13, the term “MTPX” refers to a 4× silicaselectivated H-ZSM-5/SiO₂ molecular sieve. In addition, FIG. 13 showsthat selectivation of the molecular sieve with phosphorus whileco-feeding water inhibits the unwanted methanol decomposition tosynthesis gas when used with other hydrogenation components. Forexample, a molecular sieve catalyst in accordance with the limitationsof this invention having platinum as the hydrogenation component andphosphorus as the selectivating component has a reduced methanoldecomposition to synthesis gas when water is co-feed into the reactor.

Example 16 Catalyst M

Silica-bound H-ZSM-5 (0.4 μm, 26:1 Si:Al₂) extrudate (65/35 ZSM-5/SiO₂,1/16″ cylindrical) was selectivated with silica by impregnating with 7.8wt. % Dow™-550 silicone in decane, stripping the decane, and calciningat 1000° F. This procedure was repeated two more times. The 3×selectivated material was then steamed in 100% steam at atmosphericpressure for 12 hours at 925° F.

Magnesium nitrate hexahydrate (3.61 g) was dissolved in 13.23 g ofdeionized water and added to 45 g of the steamed catalyst. After mixing,the catalyst was dried overnight at 250° F. The catalyst was thencalcined in full air at 1000° F. for 1 hour (5 vol/vol/min).

Ammonium phosphate (2.08 g) was dissolved in 13.46 g deionized water andslowly added to 37.22 g of the catalyst above. After mixing, thecatalyst was dried at 250° F. for 2 hours. The catalyst was thencalcined in full air at 660° F. for 3 hours (3 vol/vol/min).

Rhodium chloride hydrate (0.076 g) was dissolved in 9.49 g of deionizedwater and slowly added to 30 g of the catalyst above. The catalyst wasmixed well and then dried at 250° F. for 4 hours. The catalyst was thencalcined in full air at 660° F. for 3 hours (3 vol/vol/min).

The resulting catalyst had a composition of 0.1 wt. % Rh, 0.76 wt. % Mg,and 1.5 wt. % P, and an alpha value of 51, prior to incorporation of thehydrogenation component.

FIG. 14 shows the catalyst tested at different pressures, with andwithout co-feeding water. The catalyst is stable and selective.

Example 17 Steamed, 3× Silica-Selectivated H-ZSM-5/SiO₂

Silica-bound H-ZSM-5 (0.4 μm, 26:1 Si:Al₂) extrudate (65/35 ZSM-5/SiO₂,1/16″ cylindrical) was selectivated with silica by impregnating with 7.8wt. % Dow™-550 silicone in decane, stripping the decane, and calciningat 1000° F. This procedure was repeated two more times. The 3×selectivated material was then steamed in 100% steam at atmosphericpressure for 24 hours at 925° F., 975° F. and 1000° F. to form threecatalysts having alpha values of 51, 32 and 15, respectively.

Example 18 0.1% Pt/Al₂O₃

Alumina extrudate (100% Al₂O₃, 1/16″ cylindrical) was loaded with 0.1wt. % Pt by incipient wetness impregnation with tetraammine platinumnitrate, followed by drying at 250° F. and calcining for 3 hours in airat 660° F.

Example 19 Catalytic Evaluations

Catalytic data herein were obtained using a downflow fixed-bed reactorwith the following operating conditions, unless otherwise noted:Temperature=500° C., Pressure=15 psig, H₂/hydrocarbon molar ratio=0.8,pure methanol and toluene feeds at 1:3 molar ratio, WHSV=3.9 h⁻¹ basedon sieve-containing base case catalyst. The catalyst load was a mixtureof 0.4-0.8 g of 0.1% Pt/Al₂O₃ of Example 18 and 2 g for the respectivesteamed catalyst of Example 17.

Catalyst N has a catalyst load of 0.8 g of the extrudate of Example 18and 2 g of the steamed catalyst of Example 17 having an alpha value of51.

Catalyst O has a catalyst load of 0.8 g the extrudate of Example 18 and2 g of the steamed catalyst of Example 17 having an alpha value of 32.

Catalyst P has a catalyst load of 0.4 g the extrudate of Example 18 and2 g of the steamed catalyst of Example 17 having an alpha value of 15.

For the 1:3 molar feed mixture, the maximum toluene conversion expectedfrom reaction with methanol would be about 33%. Methanol utilization isreported as (moles of xylene formed−moles of benzene formed)/(moles ofmethanol converted). Benzene is subtracted to account for any xyleneformed by the disproportionation of toluene to xylene plus benzene.

As shown in FIGS. 15-17, each of Catalyst N, O and P indicate goodstability. Catalyst O appears to maintain the highest para-xyleneselectivity of 85% with toluene conversion at 7%. Catalyst P exhibitsthe highest toluene conversion at 14% with good para-xylene selectivityof 73%. This Example indicates that the hydrogenation function does nothave to be located directly on the molecular sieve to be effective inaccordance with this invention, as long as the hydrogenation function isin proximity to the molecular sieve. As shown in this example, thehydrogenation metal can be impregnated onto an amorphous support that isco-mingled with the active molecular sieve catalyst.

Example 20 0.1% Rh, 3× Silica-Selectivated, 1% P ImpregnatedZSM-5/SiO₂(Catalyst Q)

Silica bound H-ZSM-5 (450:1 Si:Al₂) extrudate (50/50 ZSM-5/SiO₂, 1/16″cylindrical) was loaded with 1 wt. % P by incipient wetness impregnationwith ammonium phosphate, drying at 250° F. and calcining for 3 hours inair at 10001F. The phosphorus containing extrudate was then selectivatedwith silica by impregnating with 7.8 wt. % DOW™-550 silicone in decane,stripping the decane, and calcining at 1000° F. This procedure wasrepeated two more times. The 3× selectivated material was then loadedwith 0.1 wt. % Rh by incipient wetness impregnation with rhodiumchloride hydrate, drying at 250° F., and calcining for 3 hours in air at660° F. The resulting catalyst had a composition of 0.1 wt. % Rh and 1wt. % P and an alpha value of 1, prior to incorporation of thehydrogenation component.

Referring now to FIG. 18, catalytic data shows that Catalyst Q maintainshigh para-selectivity and excellent catalyst stability.

1. A process for forming a selectively alkylated aromatic compoundcomprising reacting an alkylating agent with a feed comprising anaromatic compound selected from the group consisting of toluene,benzene, naphthalene, alkyl naphthalene and mixtures thereof in thepresence of a catalyst under alkylation reaction conditions, saidcatalyst comprising a selectivated molecular sieve and at least onehydrogenation metal, wherein at least one of the following conditions issatisfied: a. said selectivated molecular sieve has an alpha value ofless than 100 prior to incorporation of said at least one hydrogenationmetal, or b. said selectivated and hydrogenated molecular sieve has analpha value of less than
 100. 2. The process recited in claim 1, whereinsaid molecular sieve comprises an intermediate pore size molecularsieve.
 3. The process recited in claim 2, wherein said molecular sievecomprises a ZSM-5 molecular sieve.
 4. The process recited in claim 2,wherein said molecular sieve is selectivated by treatment with aphosphorus compound and a silicon compound.
 5. The process recited inclaim 4, wherein said silicon compound comprises silicones and siliconepolymers.
 6. The process recited in claim 5, wherein said treatment withsaid silicones and silicone polymers comprises multiple treatments withsaid silicones and silicone polymers.
 7. The process recited in claim 2,wherein said molecular sieve is selectivated by treatment with aphosphorus compound, a magnesium compound and a silicon compound.
 8. Theprocess recited in claim 7, wherein said silicon compound comprisessilicones and silicone polymers.
 9. The process recited in claim 8,wherein said treatment with said silicones and silicone polymerscomprises multiple treatments with said silicones and silicone polymers.10. The process recited in claim 1, wherein said molecular sievecomprises a zeolite-bound-zeolite molecular sieve.
 11. The processrecited in claim 10, wherein said zeolite-bound-zeolite comprises aZSM-5 core zeolite crystal bound with silica, wherein said silica binderis converted to silicalite.
 12. The process recited in claim 11, whereinsaid ZSM-5 core zeolite crystal has a silica to alumina ratio of fromabout 70:1 to 75:1 Si:Al₂.
 13. The process recited in claim 11, whereinsaid binder comprises from about 25 wt. % to about 45 wt. % based uponthe weight of said zeolite-bound-zeolite.
 14. The process recited inclaim 11, wherein said zeolite-bound-zeolite has a silica to aluminaratio of greater than 900:1 Si:Al₂.
 15. The process recited in claim 10,wherein said molecular sieve is selectivated by treatment with aphosphorus compound and a magnesium compound. 16-43. (canceled)